1. Field of the Invention
The present invention relates to a mold clamping apparatus of an injection molding machine, equipped with a drive mechanism for opening/closing and clamping a mold by use of a drive motor and a ball screw mechanism.
2. Description of the Related Art
A conventional mold clamping apparatus of an injection molding machine, equipped with a drive mechanism for opening/closing and clamping a mold by use of a drive motor and a ball screw mechanism, is disclosed in, for example, Japanese Utility Model Publication (kokoku) No. 8(1996)-1847.
The disclosed mold clamping apparatus includes a first ball nut disposed rotatably on a movable platen; a mold-clamping motor for rotating the first ball nut; a second ball screw rotatably screw-engaged with the movable platen and supported on a base; a mold-opening/closing motor for rotating the second ball screw; a first ball screw screw-engaged with the first ball nut and having a spline portion; a mold-clamping housing disposed on the base and having a hole portion formed therein in order to receive the spline portion; a support plate disposed in the vicinity of the hole portion and adapted to hold the spline portion; and a stopper plate disposed movably and adapted to stop up the hole portion.
However, the above-mentioned conventional mold clamping apparatus involves the following problems.
First, since a drive system for opening/closing the mold at high speed and a drive system for clamping the mold at high pressure are independent of each other and do not assume symmetry (equilibrium), the drive systems involve difficulty in operating smoothly and place limitations on an increase in speed of opening/closing the mold and an increase in mold clamp pressure.
Second, mechanism components are independent of each other and are dispersed; in other words, configuration or layout is not designed rationally, resulting in an increase in the overall size of the mold clamping apparatus.
An object of the present invention is to provide a mold clamping apparatus of an injection molding machine capable of operating smoothly and enabling an increase in speed of opening/closing a mold and an increase in mold clamp pressure.
Another object of the present invention is to provide a mold clamping apparatus of an injection molding machine, capable of attaining a compact overall size thereof through rational design of configuration and layout.
To achieve the above objects, the present invention provides a mold clamping apparatus of an injection molding machine, comprising a drive mechanism which, in turn, comprises a first drive mechanism for opening/closing the mold at high speed through advancement/retreat of a movable platen effected by means of a first drive motor unit and a first ball screw mechanism; a second drive mechanism for clamping the mold at high pressure through application of pressure to a pressing member effected by means of a second drive motor unit and a second ball screw mechanism; an engagement mechanism for engaging the movable platen with the pressing member in the course of advancement of the movable platen; and a clutch mechanism which is operated after establishment of the engagement effected by the engagement mechanism, in order to interlock the pressing member with the movable platen to thereby enable the pressing member to apply pressure to the movable platen.
The first drive mechanism causes the movable platen to advance/retreat, to thereby open/close the mold at high speed. In the course of advancement of the movable platen (in the course of closing the mold), the movable platen engages the pressing member via the engagement mechanism. As a result, the pressing member and the movable platen advance together. At this time, the clutch mechanism interlocks the pressing member and the movable platen so that pressure can be applied to the movable platen by means of the pressing member. Thus, as soon as the movable platen reaches a predetermined position where closing of the mold ends, the second drive mechanism can start high-pressure mold-clamping. High-pressure mold-clamping is carried out in the following manner. The second drive mechanism applies pressure to the pressing member, which, in turn, applies pressure to the movable platen via the clutch mechanism.